Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating (or dielectric) layers, conductive layers and semiconductive layers of material over a semiconductor substrate, and patterning the various layers using lithography to form circuit components and elements thereon.
A transistor is an element that is utilized extensively in semiconductor devices. There may be millions of transistors on a single integrated circuit (IC), for example. A common type of transistor used in semiconductor device fabrication is a metal oxide semiconductor field effect transistor (MOSFET).
Early MOS processes used one type of doping to create either positive or negative channel transistors. More recent designs, referred to as complimentary MOS (CMOS) devices, use both positive and negative channel devices in complimentary configurations. While this requires more manufacturing steps and more transistors, CMOS devices are advantageous because they utilize less power, and the devices may be made smaller and faster.
A nitride layer is an insulator that is often used in semiconductor device manufacturing as an etch stop layer. A nitride, such as silicon nitride (SixNy) typically etches at a lower etching rate than silicon dioxide (SiO2). Therefore, nitride materials are often used as etch stop layers to protect underlying semiconductor layers in an etch process. A nitride material layer may also be used as an endpoint detector, to indicate when an entire thickness of silicon dioxide has been etched away or removed. A different etch chemistry may then be used to remove the nitride layer. Using a nitride layer as an etch stop is advantageous in that an endpoint in the etch process can easily be determined by analyzing the by-products of the etch process, and damage to underlying material layers can be avoided.
However, in some applications, it may be undesirable to place a nitride layer or film directly over an underlying material layer. For example, depositing a tensile nitride material directly over a portion of a p channel MOS (PMOS) FET device may result in degradation of hole mobility, resulting in decreased performance of the P-type transistor.
Therefore, what is needed in the art is an etch stop material and method wherein the hole mobility of PMOS devices and other nitride-sensitive semiconductor applications is not degraded.